1. Technical Field
The present invention relates to a scan-type image display device.
2. Related Art
Recently, a scan-type image display device which displays images by performing raster scan on a light receiving surface using laser beams or other lights has been proposed. According to this scan-type image display device, two-dimensional light scan needs to be carried out by using a scanner including polygon-mirror, galvano-mirror, or the like for producing images. For the two-dimensional light scan, the scan direction of one scanner is both of horizontal and vertical directions, for example. In this case, however, the structure and control of the scanning system is complicated. For overcoming this drawback, a scan-type image display device having a pair of scanners each of which performs one-dimensional light scan has been proposed (see JP-A-1-245780). According to this scan-type image display device having the pair of the scanners, one of the scanners scans in the horizontal direction, and the other scans in the vertical direction. Light emitted from a light source passes through the scanner for horizontal scanning, and then passes through the scanner for vertical direction to travel toward the screen surface.
According to the structure using the scanner for horizontal scan and the scanner for vertical scan, however, the scan area scanned by the pair of the scanners becomes bobbin-shaped on the screen surface. This is because the optical path length from the horizontal scanner to the screen surface increases toward the upper and lower ends of the screen surface.
For converting the scan area on the screen into an appropriate rectangular area, it is possible to provide a correcting optical system between the pair of the scanners and the screen surface, or to control turn-on timing of the light source, for example.
However, the following problems arise from the scan-type image display device according to the above reference. When the correcting optical system is equipped as in the former example, lens and mirror having a not rotational curved surface and large-area are needed. Because, the scan area scanned by the pair of the scanners is large. Thus, manufacture of the display device is difficult. When the turn-on timing of the light source is controlled as in the latter example, the light utilization efficiency lowers due to the presence of periods when the light source is turned off. Moreover, the turn-on timing of the light source needs to be changed for each of the lines arranged in the vertical direction. In this case, the control circuit for controlling the turn-on timing is complicated.